The invention relates generally to lithography technology and, more particularly, to a method for fabricating a fine pattern in a photomask.
In a process of fabricating a semiconductor device, a photomask formed with a pattern is used to realize the desired pattern on a wafer. Since the pattern realized on the photomask is transferred onto the wafer through the photolithography process, the process of fabricating the photomask is very important.
In order to fabricate the photomask, a light shielding layer and a resist layer are formed on a transparent substrate and an exposure process is performed on the resist layer using an electron beam. A development process is then performed on the exposed resist layer to form a resist layer pattern that selectively exposes the light shielding layer, and the exposed portion of the light shielding layer is etched using the resist layer pattern as an etching mask to form a light shielding layer pattern. After that, the resist layer pattern is removed. As the degree of integration of semiconductor devices increases and the sizes of the patterns formed on the wafer decreases, the size of the pattern formed on the photomask also decreases. For example, in a case of a semiconductor device of 50 nm, the size of the pattern formed on the photomask must be 200 nm in consideration of 1:4 reduction exposure. However, in the case of an exposure process using an electron beam exposure apparatus, there is a limit resolution due to properties of the electron beam exposure apparatus or the resist.
With current mass production processes, it is impossible to fabricate a mask pattern of 200 nm or less which is required for fabricating the wafer pattern of 50 nm or less on the wafer and it is also difficult to fabricate the pattern below the limit resolution in the electron beam exposure process. Therefore, studies have been made for fabricating a fine pattern below the limit resolution in the electron beam exposure process.